Engines fitted with variable capacity turbochargers having a variable capacity mechanism are conventionally known. Variable capacity mechanisms include movable vanes, and by opening and closing these movable vanes the effective area of the flow channel within the exhaust gas turbine is increased and decreased. The movable vanes are controlled to open so that the effective area of the flow channel becomes large in the high rotation speed high load region when the flow rate of exhaust gas is large, and in this way an excessive rise in back pressure in the engine is suppressed. Also, the movable vanes are controlled to close so that the effective area of the flow channel becomes small in the low rotation speed low load region when the flow rate of exhaust gas is small, and in this way sufficient supercharging pressure can be obtained even in the low rotation speed low load region.
On the other hand, when the engine has been used for a long time, soot and the like is deposited near the movable parts of the variable capacity mechanism, and in some cases the movable parts can stick and become unable to move. Therefore, it is known that at predetermined timing, the movable vanes are forcibly opened and closed, to prevent the deposition of soot and the like as well as sticking of the movable parts. In Patent Document 1, the forcible opening and closing of the movable vanes in operating regions that will not directly affect the running of a vehicle, such as idling, is disclosed. Patent Document 2 discloses a method for determining a fault in the variable capacity mechanism.
Patent Document 1: Japanese Patent Application Laid-open No. 2000-265846
Patent Document 2: Japanese Patent Application Laid-open No. H11-62604